Summary

Materials and methods: In Experiment One, 144 sows were induced with
two injections of PGF 6 hours apart (split dose) with or without injection
of 20 mg DEX with the second PGF. Interval from initial PGF to farrowing, duration
of farrowing, litter size born alive, number of stillbirths, and piglet weight
gain to 10 days of age were recorded. In Experiment Two, 106 sows were induced
with single or split-dose injections of PGF with or without injection of 20
IU oxytocin 24 hours after initial PGF. Time to onset and duration of farrowing
were recorded, as were requirement for manual intervention, total litter size
born, and incidence of stillbirths.

Results: For sows farrowing 24 to 32 hours after initial PGF injection
in Experiment One, there was no effect of DEX treatment on the PGF-to-farrowing
interval, duration of farrowing, or piglet growth and survival to 10 days of
age. In Experiment Two, more sows farrowed by 32 hours after the split dose
of PGF than after a single dose (P < .05). The PGF injection protocol
did not influence the farrowing response to oxytocin. Oxytocin injection was
associated with higher stillbirth rates when cervical dilation was incomplete.

Implications: These data do not support a role for corticosteroid in
farrowing induction protocols. Oxytocin administered 24 hours after PGF (single
or split dose) was associated with farrowing problems, suggesting that routine
use of oxytocin in periparturient sows is contraindicated.

In addition to initiating piglet delivery,
peripartum endocrine changes may also affect early postnatal piglet
survival. High levels of maternal corticosteroids are
involved in advancing fetal visceral (ie, lung and intestinal) maturation, which
may
impact postnatal survival.1,2 Further,
the prepartum injection of 100 mg of prednisolone has been associated with a
reduced duration of farrowing and increased piglet survival to 3 days of
age.3 The effect on piglet survival must be interpreted
with caution, since any direct effect of cortico-steroid is confounded with effects on
duration of farrowing, although enhanced piglet neonatal growth has been observed
following a prepartum injection of 20 mg
dexameth-asone.4

The objective of induced farrowing is to allow increased supervision of piglet
delivery to improve neonatal survival.5 To
induce parturition, manufacturers recommend that a single intramuscular injection
of prostaglandin F2[alpha] (PGF) or PGF
analogue be administered up to 2 days before due date. This protocol usually results
in approximately 50% to 60% of sows farrowing the next working
day.6 However, the farrowing response was markedly
improved when two injections of PGF were administered 6 hours apart (split-dose
protocol).7 Although the predictability of
the day of farrowing was improved by the split-dose induction protocol, the time
during the day at which the sow farrowed remained variable.

To improve the synchronization of farrowing, some producers inject oxytocin 20 to
24 hours after a single PGF injection, which usually results in a more rapid delivery
of the first pig. However, this use of oxytocin also often increases the need for
manual intervention, because it is associated with
a higher incidence of interrupted
farrowings.8,9 An interrupted farrowing is
characterized by a prolonged interval between delivery
of the first pig and the subsequent piglets. Why some sows experience an
interrupted farrowing is not known. However, it
may be that the injection of oxytocin occurs before complete cervical dilation and
so results in a painful delivery of the first
piglet. In turn, pain may induce release of epinephrine and result in a transient
tocolysis. When oxytocin was administered after delivery of the first piglet and so,
presumably, after complete cervical dilation, a
shorter duration of farrowing resulted, with no evidence of interrupted
farrowings.10 From the above, we reasoned that the
improved farrowing response to a split dose of PGF suggests that more sows will have
complete cervical dilation at 24 hours after PGF
injection and so may be less likely to experience farrowing problems associated
with oxytocin treatment.

The objectives of the present experiments were to further examine the effect of
dexamethasone on the farrowing response of the sow and growth of the litter, as well
as to determine the incidence of oxytocin-associated farrowing problems after
induction with a single or split dose of PGF.

Materials and methods

Animals and facilities

These studies were approved by the animal care committees of the University of
Guelph and Michigan State University and were conducted in accordance with their
guidelines for the care and use of experimental animals. Experiment One was
conducted on each of two facilities, one a
commercial 700-sow farrow-to-feeder facility in
Guelph, Ontario, Canada, and the other a 220-sow farrow-to-finish facility at Michigan
State University. Experiment Two was conducted at the Guelph facility.

Experimental design

For Experiment One, 144 mixed-parity sows were induced to farrow 2 days before
their due date (day 113 of gestation) with two vulvar injections of 2.5 mg or 5.0 mg
prostaglandin F2[alpha] (PGF;
Lutalyse, Pharmacia, Orangeville, Ontario) administered 6 hours apart by 12-mm,
20-gauge needle. The different dosages reflect
different management protocols for each farm but, on the basis of previous
data,6 no dose-dependant difference in
farrowing response was anticipated. The initial
injection was administered between 7:00 am and 8:00
am. At the time of the second injection, sows were assigned to receive
an injection of 20 mg dexamethasone (DEX; Dexadreson, Intervet Canada,
Whitby, Ontario; n = 73) or to serve as controls
(n = 71). This dose of dexamethasone is at the high end of the therapeutic range and
was administered intramuscularly (IM) in the neck.

The following working day (24 to 32 hours after initial PGF injection), sows
were monitored continuously for piglet delivery until farrowing was complete. If an
interval between piglet deliveries exceeded 45 minutes, manual intervention was
employed. Sows farrowing < 24 hours after
initial PGF injection were not observed, and their data were not included in the
analysis. Similarly, sows farrowing > 32 hours
after initial PGF injection were deemed to be nonresponsive to the induction
protocol and excluded from data analysis. Piglets
of sows farrowing 24 to 32 hours after PGF injection were individually identified by
ear notching at birth, and incidences of piglet mortality were recorded. For sows
farrowing 24 to 32 hours after initial PGF injection, records were maintained for the
interval from initial PGF injection to onset of farrowing, duration of farrowing, litter
size born (alive and stillborn), and piglet weights and survival at birth and at 3
and 10 days of age.

For Experiment Two, 106 mixed-parity sows were assigned, 2 days before
their due-to-farrow date, to injection of 5 mg PGF (PG1; n = 29); injection of 5 mg
PGF followed 24 hours later by 20 IU oxytocin (Bimeda-MTC Pharmaceuticals,
Cambridge, Ontario) (PG1-OT; n = 28); injection of 2.5 mg PGF followed in 6 hours by a
second injection of 2.5 mg PGF (PG2; n = 24); or injection of 2.5 mg PGF followed in
6 hours by a second injection of 2.5 mg PGF and then 20 IU oxytocin 24 hours after
the initial PGF injection (PG2-OT; n = 25).

The dose of oxytocin was based on literature evidence indicating effective doses
of between 10 and 30 IU8,9,11 and
anecdotal evidence of 20 IU being a commonly used dose in commercial practice. The PGF
was administered into the vulva and the oxytocin was administered IM in the neck.
Initial PGF injections were administered between 7:00
am and 8:00 am on day 113 of gestation. During the following
working day, sows were monitored continuously for piglet delivery until farrowing was
complete. If an interval between piglet deliveries exceeded 45 minutes, manual
intervention was employed. As in Experiment One, sows farrowing < 24 hours or > 32
hours after initial PGF injection were excluded from data analysis. Where oxytocin
injection was indicated, an assessment of cervical dilation was performed prior to
injection. A gloved hand was inserted into the vagina and cervical dilation confirmed if
at least two fingers could be inserted comfortably into the cervical canal. Records
were maintained for interval from initial PGF injection to onset of farrowing, duration
of farrowing, requirement for manual intervention, and litter size born (alive and
stillborn).

Statistical analysis

All analyses were performed by ANOVA using SAS (SAS Institute Inc, Cary,
North Carolina). The treatment means for intervals from initial PGF injection to
delivery of the first pig, duration of piglet
delivery, and total born litter size were compared using the MIXED procedure. The
proportion of sows farrowing 24 to 32 hours after initial PGF injection and proportion
of stillbirths were analysed using logistic regression in GENMOD procedure
and tested by the Wald chi-square test. Differences in the variances around the
means were tested by F-ratio test and analyses were adjusted for parity. Data from
Experiment Two were analyzed as a 2 x 2 factorial.

For Experiment One, treatment effects on piglet birth weights and average daily
gain to 10 days of age were compared for all piglets using the MIXED procedure
with litter as a random effect and piglet birth weight as covariate in the model for
average daily gain. Treatment effects on mortality of piglets until 10 days of age were
tested using logistic regression in GENMOD procedure with birth weight as
covariate and accounting for the within-litter
correlation using compound symmetry correlation structure.
Separate analyses for average daily gain and mortality were
performed for all piglets with birth weight < 1.1 kg.

Results

In Experiment One, 24 sows from each treatment farrowed < 24 hours after
initial PGF injection and were not included in data analysis. Of the remaining sows,
41 DEX sows and 43 control sows commenced farrowing 24 to 32 hours after
the initial PGF injection, and the response was not affected by DEX treatment.
Eight DEX and four control sows farrowed > 32 hours after initial PGF injection and
were not included in the data analysis. Manual intervention was performed in eight
sows per treatment. For sows farrowing 24 to 32 hours after initial PGF injection, there
was no effect of DEX on the PGF-to-farrowing interval, the duration of the farrowing
process, total born litter size, stillbirth rate,
or piglet growth or mortality to 10 days of age (Table 1). Similarly, there were no effects
of DEX when analyses were restricted to piglets with birth weights < 1.1 kg.

In Experiment Two, more sows receiving two PGF injections farrowed 24 to 32
hours after initial PGF injection than did those receiving a single PGF injection
(P < .05; Table 2). There was no effect of
oxytocin treatment on numbers of sows farrowing 24 to 32 hours after PGF injection.
However, for sows farrowing 24 to 32 hours after the first PGF injection, the
variance in the interval to farrowing was less
(P < .05) for oxytocin-treated sows (Table 2).
In sows that responded to induction, there was no overall treatment effect on
the PGF-to-farrowing interval, farrowing duration, percent live births, or the need
for manual interventions (Table 2). For the eight oxytocin-treated sows that farrowed
> 32 hours after initial PGF injection, the stillbirth rate was 50%, while the
stillbirth rate was 14% for the nine sows farrowing
> 32 hours after initial PGF injection that did not receive oxytocin.

Discussion

The data presented for Experiment One indicate no effect of dexamethasone on
the timing or duration of farrowing. An earlier report had shown that prepartum
injection of prednisolone resulted in a shorter
period of piglet delivery.3 An explanation for
the shorter delivery time was not provided, but it is reasonable to infer the involvement
of an analgesic effect of the corticosteroid allowing for a more comfortable
delivery. However, the sows used in the present
study were relatively mature and so less likely to suffer a painful delivery. If true, an effect
of dexamethasone on the piglet delivery process may become apparent only in young sows.

Other authors have demonstrated that dexamethasone treatment of the
periparturient sow resulted in enhanced neonatal
piglet growth, especially of the low-birth-weight
pigs.4 Also, injection of dexamethasone into newborn piglets may improve
growth, although the effect has proven
inconsistent with either a general or a sex-linked
growth response, or no growth response being
observed.12-14 In the present study, no
effect of dexamethasone was observed on litter growth and survival regardless of
birth weight. Therefore, given the unpredictable response to corticosteroid
treatment, the use of dexamethasone in the farrowing
induction protocol does not appear to be warranted.

In Experiment Two, the farrowing response to induction supports previous reports
that the vulval route for PGF injection
produces acceptable results at lower than label
dosages.6,15 Further, in terms of the
numbers of sows farrowing 24 to 32 hours after
initial PGF injection, the split-dose PGF protocol produced a superior response compared
to the single dose, also supporting earlier
observations.7 In the present study,
oxytocin did not result in a general increase of
stillbirths in sows with a dilated cervix, but may have been a factor in the
farrowing complications and the high number of
stillbirths in sows with a closed cervix at the time of oxytocin treatment. An
increased stillbirth rate associated with the use
of oxytocin has been observed
previously.16 Since evaluation of cervical dilation is
not routinely performed prior to oxytocin injection, the prepartum use of oxytocin
cannot be recommended.

Recent research has suggested that even after delivery of the first piglet, the use
of oxytocin might produce undesirable
results.10 The latter authors described larger
numbers of stillbirths per litter, with the highest
incidence being among the first four pigs rather than towards the end of
farrowing. This pattern of stillbirth deliveries was
associated with an increased incidence of umbilical cord abnormalities,
suggesting that inappropriately powerful uterine
contractions may be detrimental to piglet survival even when the cervix is fully
patent. In the present study, oxytocin-treated
sows had numerically more farrowing problems requiring manual intervention (30
compared to 20 not requiring intervention), but
there were too few sows to detect a significant difference. This research would suggest
that there is little to be gained by routine use
of oxytocin as part of an induction program. Indeed, the potential for oxytocin to
cause problems if dilation of the cervix has not advanced sufficiently to allow easy
passage of the piglets, and its potential to cause interrupted farrowings, suggest that
the routine use of oxytocin in periparturient sows is contraindicated.

Implications

Administration of dexamethasone to periparturient sows does not
impact neonatal piglet growth or survival.

The use of a split-dose PGF induction protocol decreases the likelihood
of sows not farrowing in response to PGF.

As some sows may have a nondilated cervix 24 hours after initial
PGF injection, even with split-dose PGF induction, the use of oxytocin
in periparturient sows is contraindicated.